BRUSSELS (Reuters) - Visa Inc and Mastercard have offered to reduce the fees merchants pay when accepting card payments from tourists in an attempt to settle a long-running EU antitrust investigation and stave off possible hefty fines, people familiar with the matter said on Thursday.

Even after the reduction, such fees which are paid by merchants when they accept card payments and are a lucrative source of revenue for banks, will still likely be higher than those for EU cards, they say.

The European Commission has battled for more than a decade to reduce such costs and encourage cross-border trade and online commerce. Regulators across the Atlantic have also frowned on such practices.

Visa, the world's largest payments network operator found itself in the Commission's crosshairs in August 2017, charged with subjecting the cards of foreign tourists to excessive fees when they used in the EU.